Lateral Lumbar Interbody Fusion (LLIF) Surgery, Psoas Muscle Size Changes, and Clinical Findings: Do they Correlate?

Introduction: Lateral Lumbar Interbody Fusion (LLIF) is a minimally invasive fusion technique seeking to reduce soft tissue damage as compared to similar alternatives. However, major concerns have been raised over nerve injury after LLIF, with reported postoperative concerns over sensory deficits and iliopsoas weakness. This study sought to determine if LLIF is associated with a change in psoas muscle size, postsurgical hip flexor (HF) weakness, or lower extremity numbness after surgical intervention.

Methods: We conducted a retrospective review of LLIF-consecutive patients at our institution from 2016 to present. Cross-sectional area of the psoas was measured bilaterally at mid-body of L3. Change from preoperative to postoperative ipsilateral and contralateral measurements of psoas area, HF strength, and numbness were compared. Postoperative imaging was required to be at least one month after the surgery.

Results: Ninety-three LLIF patients met our initial criteria, and 37 (40%) had imaging available for comparison. Ninety-three LLIF patients met our initial criteria, and we used a matched cohort of 27 patients with CT patients and 27 with MRI. On CT imaging, there was a significant decrease in ipsilateral psoas area (p=0.05) after LLIF but no significant change in contralateral psoas area. Contralateral HF strength increased postoperatively at least one grade (p=0.04), but no significant changes in ipsilateral HF strength, numbness, or contralateral numbness were found. Of the 32 patients with documented symptoms, 9.6% (n = 9) of patients reported preoperative numbness and a different 9.6% reported postoperative numbness (n = 9). Resolution of postoperative symptoms occurred between 1 to 7 months (2.47 ± 1.97), except for three patients who required further surgery.

Conclusion : LLIF may be associated with decreases in ipsilateral psoas size. Our study showed no significant correlation in ipsilateral numbness or weakness after LLIF and change in psoas size, though future studies with greater sample size may be helpful to support these findings.